Consolidated Statement of Changes in Shareholders Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions		Total	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]	Preference Stock Not Subject To Mandatory Redemption [Member]	PECO Energy Co [Member]	PECO Energy Co [Member] Common Stock [Member]	PECO Energy Co [Member] Retained Earnings [Member]	PECO Energy Co [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Exelon Generation Co L L C [Member]	Exelon Generation Co L L C [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Exelon Generation Co L L C [Member] Noncontrolling Interest [Member]	Exelon Generation Co L L C [Member] Membership Interest [Member]	Exelon Generation Co L L C [Member] Undistributed Earnings [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member] Common Stock [Member]	Commonwealth Edison Co [Member] Other Paid-In Capital [Member]	Commonwealth Edison Co [Member] Retained Deficit Unappropriated [Member]	Commonwealth Edison Co [Member] Retained Earnings Appropriated [Member]	Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member] Common Stock [Member]	Baltimore Gas and Electric Company [Member] Retained Earnings [Member]	Baltimore Gas and Electric Company [Member] Membership Interest [Member]	Baltimore Gas and Electric Company [Member] Preference Stock Not Subject To Mandatory Redemption [Member]
Beginning Balance at Dec. 31, 2012		$ 21,730	$ 16,632	$ (2,327)	$ 9,893	$ (2,767)	$ 106	$ 193															$ 2,358	$ 1,360	$ 808	$ 2,168	$ 190
Beginning Balance (in shares) at Dec. 31, 2012		889,525
Beginning Balance at Dec. 31, 2012									$ 2,982	$ 2,388	$ 593	$ 1						$ 7,323	$ 1,588	$ 5,014	$ (1,639)	$ 2,360
Beginning Balance at Dec. 31, 2012													$ 12,665	$ 513	$ 108	$ 8,876	$ 3,168
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 1,729			1,719		(10)	20	395		395		1,060		(10)		1,070	249			249		210		210	210
Long-term incentive plan activity, shares		1,445
Long-term incentive plan activity		$ 81	81
Employee stock purchase plan issuances		$ 28	28
Employee stock purchase plan issuances, shares		1,064
Common stock dividends		$ (1,254)			(1,254)			(6)	(332)		(332)							(220)				(220)
Common stock issuance Constellation merger, shares		0
Consolidated VIE dividend to noncontrolling interest		$ (63)	0				(63)
Deconsolidation of VIE		(18)	0				(18)						(19)		(18)	(1)
Redemption of preferred securities		(6)						0	(6)		(6)
Preferred and preference stock dividends		(14)						(14)	(1)		(1)												(13)		(13)	(13)
Other comprehensive income, net of income taxes		727											(299)	(299)				7,528
Acquisition of noncontrolling interest													(63)		(63)
Tax benefit on stock compensation		44
Acquisition of noncontrolling interest													3			3
Other comprehensive loss, net of income taxes		727				727
Distribution to member													(625)				(625)
Allocation of tax benefit from member													26			26
Parent tax matter indemnification									27	27								176		176
Appropriation of retained earnings for future dividends																					(249)	249
Ending Balance at Dec. 31, 2013		$ 22,940	16,741	(2,327)	10,358	(2,040)	15	193															2,555	1,360	1,005	2,365	190
Ending Balance (in shares) at Dec. 31, 2013		892,034
Ending Balance at Dec. 31, 2013									3,065	2,415	649	1							1,588	5,190	(1,639)	2,389
Ending Balance at Dec. 31, 2013													12,742	214	17	8,898	3,613
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Allocated Share-based Compensation Expense, Net of Tax		$ 74
Net income		$ 1,820			1,623		184	13	352		352		1,019		184		835	408			408		211		211	211
Long-term incentive plan activity, shares		1,574
Long-term incentive plan activity		$ 72	72
Employee stock purchase plan issuances		$ 35	35
Employee stock purchase plan issuances, shares		960
Common stock dividends					0				(320)		(320)							(307)				(307)
Consolidated VIE dividend to noncontrolling interest													421		421
Deconsolidation of VIE													(1,548)		(1,548)
Preferred and preference stock dividends		$ (131)						0															(13)		(13)	(13)
Other comprehensive income, net of income taxes	[1]	(644)											(250)
Acquisition of noncontrolling interest		(421)				0	(421)
Common stock dividends		(1,071)			(1,071)		0
Preferred and preference stock dividends		(13)						(13)
Tax benefit on stock compensation		47
Acquisition of noncontrolling interest		4	(2)				6						(5)		(5)
Fair value of financing contract payments			(131)
Transfer of CENG pension and non-pension postretirement benefit obligations		(2)	(2)
Reversal of CENG equity method AOCI, net of income taxes		(116)
Other comprehensive loss, net of income taxes		(528)				(528)							(134)	(134)
Distribution to member													(645)				(645)
Allocation of tax benefit from member													53			53
Noncontrolling interest acquired		(1,548)					(1,548)						(116)	116
Parent tax matter indemnification									24	24								5		5
Appropriation of retained earnings for future dividends																					(408)	408
Contribution from parent		273																		273
Ending Balance at Dec. 31, 2014		$ 24,133	16,709	(2,327)	10,910	(2,684)	1,332	193															2,753	1,360	1,203	2,563	190
Ending Balance (in shares) at Dec. 31, 2014		894,568
Ending Balance at Dec. 31, 2014		$ 22,608							3,121	2,439	681	1						7,907	1,588	5,468	(1,639)	2,490	2,563
Ending Balance at Dec. 31, 2014													14,051	(36)	1,333	8,951	3,803
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options		(8)	8
Allocated Share-based Compensation Expense, Net of Tax		80
Net income		$ 2,250			2,269		(32)	13	378		378		1,340		(32)		1,372	426			426		288		288	288
Long-term incentive plan activity, shares		1,430
Long-term incentive plan activity		$ 70	70
Employee stock purchase plan issuances		$ 32	32
Employee stock purchase plan issuances, shares		1,170
Common stock dividends		$ (1,111)			(1,111)				(279)		(279)							(299)				(299)	(158)		(158)	(158)
Preferred and preference stock dividends		(13)						(13)															(13)		(13)	(13)
Other comprehensive income, net of income taxes		60											(27)
Tax benefit on stock compensation		46
Acquisition of noncontrolling interest		(4)	0				(4)						(1)		(2)	1
Temporary Equity, Other Changes		4					4						4		4
Other comprehensive loss, net of income taxes		60				60							(27)	(27)
Distribution to member													(2,474)				(2,474)
Allocation of tax benefit from member													47			47
Noncontrolling interest acquired													(32)
Parent tax matter indemnification									16	16								7		7			7	7		7
Appropriation of retained earnings for future dividends																					(426)	426
Contribution from parent		202																		202
Ending Balance at Dec. 31, 2015		$ 27,294	18,676	$ (2,327)	$ 12,068	$ (2,624)	$ 1,308	$ 193															2,877	$ 1,367	$ 1,320	$ 2,687	$ 190
Ending Balance (in shares) at Dec. 31, 2015		954,668
Ending Balance at Dec. 31, 2015		$ 25,793							$ 3,236	$ 2,455	$ 780	$ 1						$ 8,243	$ 1,588	$ 5,677	$ (1,639)	$ 2,617	$ 2,687
Ending Balance at Dec. 31, 2015													$ 12,942	$ (63)	$ 1,307	$ 8,997	$ 2,701
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		57,500
Stock Issued During Period, Value, New Issues		$ 1,868	$ 1,868
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options		(3)
Allocated Share-based Compensation Expense, Net of Tax		$ 73

[1] All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.